Projection screens are often employed to enhance the display of light projected from projectors by reflecting the light to be viewable by one or more people. Conventional projection screens, however, are particularly susceptible to contrast ratio degradation because typical projection screens reflect ambient light as readily as the image projected from projectors.
The contrast ratio is the ratio of the brightness of a white pixel to the brightness of a black pixel. A black pixel is generally as white as the ambient lighting because conventional projection screens are typically highly reflective. As such, ambient light incident upon the projection screen is often reflected back to the viewer, thereby reducing the contrast ratio of the image projected from projectors.
Prior approaches to reducing the effects of ambient light have been to use gray screens to improve the contrast level. However, this technique also reduces the overall brightness of the intended image. Accordingly, conventional gray screens require the use of relatively more expensive projectors having substantially higher-powered light sources capable of casting more light to compensate for the reduction in overall brightness.
Other conventional techniques involve various techniques that have the effect of focusing more of the reflected projector light into a limited viewing cone, which is called “screen gain”. Outside of this viewing cone, the picture quality drops, while inside the viewing cone, the brightness is increased with limited effect on improving the contrast ratio, as the ambient light is also affected by the screen gain. Some high-gain projection screens have utilized an array of lenses over a reflective background to direct projected light back to a viewer. Although these screens preferentially reject ambient light with respect to projected light, they suffer from a severely limited viewing angle and are associated with relatively high costs.